There are several similar species, including the partly sympatric Arctic tern, which can be separated on plumage details, leg and bill colour, or vocalisations.

Breeding in a wider range of habitats than any of its relatives, the common tern nests on any flat, poorly vegetated surface close to water, including beaches and islands, and it readily adapts to artificial substrates such as floating rafts.

Like most terns, this species feeds by plunge-diving for fish, either in the sea or in freshwater, but molluscs, crustaceans and other invertebrate prey may form a significant part of the diet in some areas.

Eggs and young are vulnerable to predation by mammals such as rats and American mink, and large birds including gulls, owls and herons.

Its large population and huge breeding range mean that this species is classed as being of least concern, although numbers in North America have declined sharply in recent decades.

Despite international legislation protecting the common tern, in some areas, populations are threatened by habitat loss, pollution, or the disturbance of breeding colonies.

They are gull-like in appearance, but typically have a lighter build, long pointed wings (which give them a fast, buoyant flight), a deeply forked tail, slender legs,[3] and webbed feet.

[5] The common tern was first described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae under its current scientific name, Sterna hirundo.

The Latin for swallow is hirundo, and refers here to the tern's superficial likeness to that unrelated bird, which has a similar light build and long forked tail.

A major moult to adult breeding plumage occurs in the next February to June, between forty and ninety per cent of feathers being replaced.

The common tern has a larger head, thicker neck, longer legs, and more triangular and stiffer wings than its relative, and has a more powerful, direct flight.

[26][27] The trailing edge of the outer flight feathers is a thin black line in the Arctic tern, but thicker and less defined in the common.

The alarm call doubles up as a warning to intruders, although serious threats evoke a kyar, given as a tern takes flight, and quietens the usually noisy colony while its residents assess the danger.

[37] A down-slurred keeur is given when an adult is approaching the nest while carrying a fish, and is possibly used for individual recognition (chicks emerge from hiding when they hear their parents giving this call).

[53] A bird ringed at the nest in Sweden was found dead on Stewart Island, New Zealand, five months later, having flown an estimated 25,000 km (15,000 mi).

Stray birds have been found inland in Africa (Zambia and Malawi), and on the Maldives and Comoros islands;[55] the nominate subspecies has reached Australia,[35] the Andes, and the interior of South America.

[45] It avoids areas which are frequently exposed to excessive rain or wind, and also icy waters, so it does not breed as far north as the Arctic tern.

[45] On their return to the breeding sites, the terns may loiter for a few days before settling into a territory,[66] and the actual start of nesting may be linked to a high availability of fish.

[68] Inbreeding among close S. hirundo relatives appears to be avoided passively by immigration and dispersal rather than by kin discrimination and mate choice.

[70] Pairs are established or confirmed through aerial courtship displays in which a male and a female fly in wide circles up to 200 m (660 ft) or more, calling all the while, before the two birds descend together in zigzag glides.

[71] The eggs may be laid on bare sand, gravel or soil, but a lining of debris or vegetation is often added if available,[45] or the nest may be rimmed with seaweed, stones or shells.

[77] The precocial downy chick is yellowish with black or brown markings,[72] and like the eggs, is similar to the equivalent stage of the Arctic tern.

[60][88] The species caught depend on what is available, but if there is a choice, terns feeding several chicks will take larger prey than those with smaller broods.

[97] The proportion of fish fed to chicks may be as high as ninety-five per cent in some areas, but invertebrate prey may form a significant part of the diet elsewhere.

[5] Chicks do not drink before fledging, reabsorbing water, and, like adults, excreting excess salt in a concentrated solution from a specialised nasal gland.

[5] Rats will take tern eggs, and may even store large numbers in caches,[105] and the American mink is an important predator of hatched chicks, both in North America, and in Scotland where it has been introduced.

[5][111] Merlins and peregrine falcons may attack flying terns; as with other birds, it seems likely that one advantage of flocking behaviour is to confuse fast-flying predators.

[5][106] Although some Eurasian populations are stable, numbers in North America have fallen by more than seventy per cent in the last forty years, and there is an overall negative trend in the global estimates for this species.

[91] Threats come from habitat loss through building, pollution or vegetation growth, or disturbance of breeding birds by humans, vehicles, boats or dogs.

The plan is intended to address key issues such as species and habitat conservation, management of human activities, research, education, and implementation.